Embryo freezing is a well-established form of assisted conception treatment. An increasing number of IVF clinics worldwide are now able to freeze spare embryos for later transfer. The first frozen embryo baby was born in 1984. Embryo cryopreservation allows multiple embryo transfers from a single egg collection and improves the chances of livebirth.
Embryos can be frozen at any stage (pronucleate, early cleaved and blastocyst) if they are of good quality. Embryos are stored in batches of one or more embryos depending on the number of embryos that are likely to be transferred into the uterus at a later date.
Embryos are mixed with a cryoprotectant fluid (to protect embryos from damage during freezing process). Then, the mixture is put either in a plastic straw or a glass ampoule and stored in liquid nitrogen at a very low temperature -196°C using a specialized programmable machine.
Thawing of embryo involves removing the embryos from the liquid nitrogen, thaw at room temperature, remove the cryoprotectant fluid and mix the embryo in a special culture media. The mixture is then kept in the incubator ready for transfer.
If the embryos were frozen at cleaved stage or blastocyst, they can be thawed and replaced in the same day. However, if they were frozen at the two-pronucleate stage, then they are thawed on the day before and cultured overnight to allow them to divide and are replaced when they become 2-4 cell embryo (s).
Not all embryos survive the freezing and thawing process. In a good freezing program, a survival rate of 75-80% should be expected. Therefore, it may be necessary to thaw out several embryos to get two or three good embryos to replace. Damage of embryos does occur as a result of freezing, not during the storage but during the cooling and thawing process.
* It is important that both the couple and the clinic to keep in contact with regard their frozen embryos.
Five years in the first instance. You can extend the storage period for another five years providing you have renewed your consent to enable us to do so. There is no known deterioration in the health of the embryo with time.
Frozen/thawed embryos may be transferred into the uterus in a natural cycle, a hormone replacement cycle or a stimulated cycle. In general, the three methods have similar pregnancy and live birth rates.
This is usually recommended in young women with regular menstrual cycles and ovulation. It involves serial ultrasound scans to check the development of the follicle and endometrium, blood tests to check the levels of hormone LH, estrogen and progesterone. Embryo transfer is usually performed about 3-4 days after the LH surge (2-3 days after ovulation). The woman is given no drugs until the day of embryo transfer. On the day of embryo transfer, the woman may start a course of progesterone pessaries or tablets to support the luteal phase.
This is usually recommended for older women, woman without ovaries or non-functioning ovaries, women with irregular infrequent menstrual cycles or ovulation. It involves giving estrogen in the form of tablets or skin batches and later adds progesterone in the form of tablets, pessaries, gel or injection. Different IVF clinics have different protocols for giving these medications and in some women GnRh agonists may be given in addition to hormone replacement to “switch off” any hormone production by the ovaries which may interfere with the treatment. After embryo transfer, both estrogen and progesterone are continued until the pregnancy test. In the test is positive, the woman should continue the medication for a further 8-10 weeks.
This is where fertility drugs such as clomid tablets or FSH injection is given aiming to produce one or two follicles. When the follicle is mature and the endometrium developed satisfactorily, hCG injection is given to induce ovulation. Embryo transfer is usually performed 2-3 days after the ovulation. This regimen is usually recommended for women do not ovulate regularly and did not respond to hormone replacement treatment in a previous cycle.
The transfer of frozen embryo result in a lower pregnancy and live birth rates than fresh embryo transfer. The risk of multiple pregnancy is also lower. In CFC , the pregnancy and live birth rates after transfer of frozen embryos compared favorably with that achieved after fresh embryo transfer. The live birth rate per embryo transfer cycle is around 30%. The success rates depend on many factors; mainly the woman’s age and number of embryos transferred. The outcome of pregnancies resulted from frozen embryo transfer is similar to fresh embryo transfer in the incidence of miscarriage, ectopic pregnancy, preterm deliveries and term deliveries. To date there is no evidence that babies born after frozen embryo transfer have any increased incidence of congenital abnormality.
Sperm can be stored for a number of reasons, including:
Sperm is stored in a similar way to that referred to above for embryo freezing. Sperm can be kept in storage for up to 15 years depending on the circumstances.
Human Oocyte cryopreservation is a rapidly advancing, breakthrough technology in which a woman’s oocytes are extracted, frozen and stored. Later, when she is ready to become pregnant, the eggs can be thawed, fertilized, and transferred to the uterus as embryos.
Women diagnosed with cancer who have not yet begun chemotherapy or radiotherapy; Chemotherapy and radiotherapy are toxic for oocytes, leaving few, if any, viable eggs. Egg freezing offers women with cancer the chance to preserve their eggs so that they can have children in the future.
Women undergoing assisted reproductive technologies who object, either for religious or ethical reasons, to the practice of freezing embryos. Having the option to fertilize only as many eggs as will be utilized in the IVF process, and then freeze any remaining unfertilized eggs can be a positive solution. In this way, there are no excess embryos created, and there need be no disposition of unused frozen embryos, a practice which can create complex choices for certain individuals.
Women who would like to preserve their future ability to have children, either because they do not yet have a partner, or for other personal or medical reasons. Egg freezing can also be beneficial for women who, for the purpose of education, career or other reasons, desire to postpone childbearing. Freezing eggs at an early age may ensure a chance for a future pregnancy.
Additionally, women with a family history of early menopause have an interest in fertility preservation. With egg freezing, they will have a frozen store of eggs, in the likelihood that their eggs are depleted at an early age.
The egg-retrieval process for oocyte cryopreservation is the same as that for in vitro fertilization. When the eggs have matured, additional hormone is given and the eggs are removed with an ultrasound-guided needle through the vagina. The procedure is conducted under sedation. The eggs are immediately frozen.
Eggs are frozen using either a slow-freeze method or a flash-freezing process known as vitrification. The slow-freeze method is the most studied and is most similar to current embryo freezing techniques. Vitrification is a rapid freezing process in which a high concentration of cryoprotectant is used. The result is a solid glass-like cell, free of ice crystals. There are differing schools of thought on which freezing method is superior, though both methods have availed acceptable pregnancy rates.
Approximately 200 births resulting from frozen eggs have been documented worldwide. Among these births, the rate of birth defects and chromosomal defects has been consistent with that of the general population.
